The present invention relates, in general, to a pressure responsive type brake actuator for use on railway, or other similar type, vehicles and, more particularly, this invention relates to a tread brake actuator having a power and a slack adjuster collet that enables automatic slack adjustment using fewer operating components.
Currently used tread brake actuators employ a plurality of brake adjusting components in the form of nuts, ratchets, clutches and springs to compensate for wear of both the wheel tread and friction material of a brake shoe. FIG. 3 of the drawings in the present application is a cross sectional view of such type brake actuator.
Another and older type tread brake actuator is shown in U.S. Pat. No. 3,995,537 to Severinsson. In both of these devices, a fluid responsive piston moves in a direction perpendicular to a push rod that operates to apply brake shoes directly to tread surfaces of railway vehicle wheels. Slack adjustments in the brake unit of the Severinsson patent are manually made by a nut disposed on components located outside of a housing containing the piston and push rod of the brake unit. The disclosure of this patent is incorporated herein by reference thereto.
U.S. Pat. No. 5,423,401 to Noah et al., which is assigned to the assignee of the present application, discloses power and slack adjuster collets located on a push rod of a disc type brake actuator. The disclosure of this patent is also incorporated herein by reference thereto.
The present invention uses collet structures, similar to those disclosed in the Noah et al. patent, in a tread brake unit and thereby eliminates the multiple components of currently available tread brake units for adjusting for wear of brake material and wheel surfaces. More particularly, the invention employs two housing structures respectively located about the slack adjuster and power collets. The power collet housing provides a bearing surface that forces the power collet into engagement with an externally threaded push rod when air pressure is received by a brake applying piston. The slack adjuster collet and its housing, which is fixed, have a clearance between them that corresponds to a typical clearance provided between the brake shoe and wheel surface. The push rod is translated by the power collet to apply the brake shoe to the wheel surface and causes the slack adjuster collet to move until the brake shoe engages the wheel surface under a braking force or until the slack adjuster collet contacts its housing. Such contact occurs when the distance the push rod must travel to apply such braking force exceeds the original clearance of the brake shoe and wheel. This contact causes the slack adjuster collet to stop while the push rod continues to travel through the slack adjuster collet and its associated housing. When air pressure is released, the piston moves away from the brake applying position under force of a spring and the housing of the power collet returns to its original position due to the action of another spring. The return action of the housing of the power collet pulls the power collet in a rearward direction which pulls the push rod and slack adjuster collet rearwardly until the slack adjuster collet contacts its housing at the end opposite the brake applying end of the housing. When contact is made the slack adjuster collet stops and holds the push rod, thus preventing further rearward movement of the push rod. The actuator is now adjusted to the increased brake shoe/wheel surface clearance due to wear. If the power collet is not in a fully retracted position it will continue to move after the slack adjuster collet contacts its housing, as the power collet is now free to slide on the push rod until the power collet housing is in a fully retracted position.
It is, therefore, a primary object of the present invention to use a slack adjusting collet similar to that of the above noted Noah et al. patent in tread brake units in place of currently used slack adjusting nuts, ratchets and clutches in order to significantly reduce the number of slack adjusting components required in a tread brake unit.
Another object of the present invention is to provide a railway and/or other similar type vehicle fluid pressure operated tread brake actuator having an improved collet style slack adjusting mechanism which is significantly more maintenance free than previously used slack adjusting components.
Still another object of the present invention is to provide a railway and/or other similar type vehicle fluid pressure operated tread brake actuator having an improved collet style slack adjusting mechanism which is generally less expensive to manufacture due to significantly reduced assembly time required compared to the time required to assemble previously used tread brake actuators.
Yet another object of the present invention is to provide a railway and/or other similar type vehicle fluid pressure operated tread brake actuator having a collet style slack adjusting mechanism that does not require special equipment to install.
A further object of the present invention is to provide a railway and/or other similar type vehicle fluid pressure operated tread brake actuator having a collet style slack adjusting mechanism that is lighter in weight than previously used slack adjusters.
It is an additional object of the present invention to provide a railway and/or other similar type vehicle fluid pressure operated tread brake actuator having a collet style slack adjusting mechanism that exhibits a long operating life.
In addition to the objects and advantages of the present invention described above, various other objects and advantages of the invention will become more readily apparent to those persons skilled in the relevant art from the following more detailed description of the invention, particularly, when such description is taken in conjunction with the attached drawing FIGS. and with the appended claims.